This invention relates generally to liquid hydrocarbon stabilizers, and more particularly to liquid hydrocarbon stabilizers containing hindered phenols and peroxide decomposers, and to methods of treating liquid hydrocarbons with liquid hydrocarbon stabilizers.
Hydrocarbon liquids, such as distillate fuels (gasoline, diesel fuel, and jet fuel), kerosene, and solvents are known to undergo reactions in the presence of oxygen. These reactions, called autoxidation, increase with temperature and extended storage time and result in the formation of oxidized products, specifically hydroperoxides. Oxidation is especially likely with liquid hydrocarbons that are strongly hydrotreated and those that are low in sulfur.
Distillate fuels contain varying amounts of natural oxidation inhibitors that prevent the formation of peroxides. However, these natural antioxidants may not always be present in sufficient quantities to prevent formation of peroxides. In addition, naturally occurring antioxidants are often removed from fuels by refinery treatment processes. Many solvents and kerosene essentially lack any natural antioxidants.
Hydroperoxides are known to be detrimental to fuel system components, such as xe2x80x9cOxe2x80x9d rings and gasket materials. They cause premature aging of these components, and the degradation of the elastomeric seals can result in fuel leaks and costly maintenance. Fuel leaks are not only an environmental problem due to the release of volatile hydrocarbons into the environment, they also present a substantial safety risk as a result of the threat of fire from fuel leaks near hot engine components.
In 1993, California specified substantially reduced sulfur containing compounds in diesel fuel. The xe2x80x9clow sulfurxe2x80x9d diesel fuel created significant fuel/material interaction problems. The problems appear to be related to the formation of peroxides in the diesel fuels during storage, particularly in tanks on diesel trucks which can keep the diesel fuel at temperatures sometimes as high as 300xc2x0 F. As a result of these problems, California rescinded the low sulfur standard (less than 10 ppm) in favor of a 50 ppm sulfur standard, but the higher sulfur standard means a higher level of pollution. The U.S. Environmental Protection Agency is considering a new sulfur standard, making it likely the issue will arise again.
Many attempts have been made to solve the problem of oxidation of liquid hydrocarbons. The introduction of additives into liquid hydrocarbons has been used successfully for many years. The U.S. Air Force JP-8+100 program developed an additive package for jet fuel which significantly increases the thermal stability of the fuel, preventing the formation of deposits which result from fuel oxidation within aircraft fuel systems. See Heneghan, S. P., Zabarnick, S., Ballal, D. R., Harrison, W. E., J. Energy Res. Tech. 1996, 118, 170-179; and Zabarnick, S., and Grinstead, R. R., Ind. Eng. Chem. Res. 1994, 33, 2771-2777.
Other examples include U.S. Pat. No. 5,382,266, which teaches the application of phosphine and phosphates to distillate fuels to prevent fuel degradation (color degradation, particulate formation, and/or gum formation), and U.S. Pat. No. 5,509,944 which discloses the stabilization of gasoline by adding an effective amount of a primary antioxidant, such as phenylene diamine, a hindered monophenol, or mixtures of these, and a secondary antioxidant, such as dimethyl sulfoxide. The combination of phosphine and hindered phenols has been used as a stabilizer in thermoplastic polymers to prevent discoloration. See, U.S. Pat. No. 5,362,783.
There remains a need for an improved stabilizer to inhibit the oxidation and formation of peroxides in liquid hydrocarbons. There is a need for n stabilizer which improves the storage stability and consequent fuel/material incompatibilities in liquid hydrocarbons.
The present invention meets these needs by providing a liquid hydrocarbon stabilizer containing a combination of additives. The liquid hydrocarbon stabilizer includes a hindered phenol, and a peroxide decomposer selected from sulfides having a general formula R4xe2x80x94Sxe2x80x94R5 and phosphine compounds having a general formula PR6R7R8 where R4, R5, R6, R7, and R8 are the same or different and are each alkyl, aryl, alkylaryl, arylalkyl, hydroxyalkyl, hydroxyaryl, hydroxyalkylaryl, hydroxyarylalkyl groups, or heteroatomic alkyl, aryl, alkylaryl, arylalkyl, hydroxyalkyl, hydroxyaryl, hydroxyalkylaryl, hydroxyarylalkyl groups containing nitrogen, sulfur, or oxygen.
The hindered phenol preferably has the general formula 
where R1, R2, and R3 are the same or different and are each alkyl, aryl, alkylaryl, arylalkyl, hydroxyalkyl, hydroxyaryl, hydroxyalkylaryl, hydroxyarylalkyl groups, or heteroatomic alkyl, aryl, alkylaryl, arylalkyl, hydroxyalkyl, hydroxyaryl, hydroxyalkylaryl, hydroxyarylalkyl groups containing nitrogen, sulfur, or oxygen and where at least one of R1 and R2 provide stearic hindrance. R1 and/or R2 are preferably isobutyl or tertiary butyl groups. The hindered phenol is preferably either 2,6-di-tert-butyl-4-methylphenol or 6-tert-butyl-2,4-dimethylphenol. The to hindered phenol is preferably present in an amount in the range of from about 5 to about 50 mg/l.
The preferred sulfide compound is hexyl sulfide, and the preferred phosphine compound is triphenylphosphine.
The peroxide decomposer is preferably present in an amount less than about 10 g/l. When triphenylphosphine is used, it is preferably present in an amount of from about 20 to about 250 mg/l.
The present invention also includes a method of treating a liquid hydrocarbon by introducing a liquid hydrocarbon stabilizer as described into the liquid hydrocarbon.
Accordingly, it is an object of the present invention to provide a new and improved stabilizer to inhibit oxidation and formation of peroxides in liquid hydrocarbons and to provide a method of using such stabilizers. These and other objects, features and advantages of the present invention will become apparent from the drawings, detailed description and claims.